The source linked debugger provides a set of buttons to allow you to move from port to port while debugging. The debugger's travel commands are described in dbg-bas-tra; these buttons are labeled with the names of the commands, so using them should be straightforward.
+-----+----+----+---+----------+-----+----+- +----------+
|Creep|Skip|Leap|Zip|Quasi-skip|Retry|Fail| ... |Frame Back|
+-----+----+----+---+----------+-----+----+- +----------+
When framed up, the skip, retry, and fail buttons operate relative to the invocation shown. Framing up is explained in dbg-sld-anc.